The present invention relates in general to the field of eyeglasses and more particularly to preparing an ophthalmic lens for shaping by edging.
More particularly, the invention relates to a device for preparing an ophthalmic lens for machining, the device comprising:                a support suitable for holding said ophthalmic lens;        blocking means including at least one blocking accessory and a manipulator arm for manipulating said blocking accessory;        an acquisition device suitable for acquiring an image of the ophthalmic lens held by the support; and        electronic and/or computer processor means suitable firstly for deducing an optical frame of reference of the ophthalmic lens from the image acquired by the acquisition device, and secondly for controlling the position of the manipulator arm and/or of the support to apply said blocking accessory against the ophthalmic lens in a given blocking position that depends on the deduced optical frame of reference.        
The invention also provides a method of preparing an ophthalmic lens by means of such a preparation device.
The technical part of the profession of an optician consists in mounting a pair of ophthalmic lenses that are ready for shaping in a frame selected by a wearer. Such mounting comprises three main operations:                acquiring the shape of the bezel of each of the two rims of the eyeglass frame if the frame is of the rimmed type (i.e. acquiring the shapes of the grooves that run around the inside of each rim of the frame); or acquiring the shape of a presentation lens or of a template if the frame is of the half-rimmed or pierced type;        centering each lens, which consists in determining the position that each lens is to occupy in the frame so as to be suitably centered in register with the pupil of the wearer's eye so as to perform appropriately the optical function for which it is designed; and        shaping each lens, which consists in machining or cutting out its outline to the shape that is desired, given firstly the shape that has been acquired from the bezel or the presentation lens or the template, and secondly the defined centering parameters.        
The present invention relates more particularly to the second operation that is known as “centering”. Specifically, the optician needs to define the position that is to be occupied by the final outline to which the lens is to be shaped relative to the optical frame of reference of said lens (typically, its usual marks or its optical centering point), so that once the lens has been assembled with the frame, it is suitably positioned in register with the pupil of the wearer's eye.
To do this, the optician begins by taking measurements from the wearer and the frame selected by the wearer in order to determine in particular the positions of the wearer's eyes relative to the frame, and thus relative to the final outline.
Then, in a second stage, the optician places the lenses on a lens support provided on a preparation device of the type defined in the introduction. The acquisition device of that preparation device then acts on each lens to determine the position of its optical centering point for positioning in register with the pupil of one of the eyes of the wearer.
In a third stage, the electronic and/or computer processor means of the preparation device deduce the position of the final outline on each lens for shaping as a function of the positions determined for the centering points and of the measured positions of the pupils of the wearer's eyes relative to the final outline. Depending on the position of the final outline on each lens, the processor means act for each lens to define both a blocking point and a blocking axis (situated in the mean plane of the lens).
Finally, during a last stage, a blocking accessory of the preparation device is stuck onto each lens at its blocking point, and in an orientation that is a function of the determined blocking axis. In this way, each lens can subsequently be extracted from the preparation device and then placed in a shaper device, with the frames of reference of the lenses being conserved by the positions of the blocking accessories on the lenses. The blocking accessories are stuck automatically in place by means of the manipulator arm, which is adapted to move relative to the ophthalmic lens support.
Nevertheless, the Applicant has found that in spite of the care given to making and assembling the structural and optical elements of the preparation device, once the ophthalmic lenses have been shaped, it can happen that they are not properly centered on the axes of the wearer's eyes, which can lead to visual discomfort for the wearer.